How to easily disable theme changing

paste the following piece of code in your functions.php file:

add_action('admin_init', 'slt_lock_theme'); 
 function slt_lock_theme() { 
     global $submenu, $userdata;  
get_currentuserinfo();  
    if ($userdata->ID != 1) {  
        unset($submenu['themes.php'][5]); 
     set($submenu['themes.php'][15]);  
    } 
 }